I. Field of the Invention
The present invention relates to a method and system for reducing angular noise in the processing of radar signals. More specifically, the present invention relates to a novel and improved method and system for estimating target angle information by adaptively reducing target induced glint in radar signals reflected from the target, especially in radar systems employed in line of sight (LOS) rate tracking loop applications.
II. Background Art
In conventional radar tracking systems, a target is generally tracked by virtue of the entire target radar return signal. Furthermore, radar tracking systems are generally employed to track targets such as aircraft or missiles, which are generally complex in shape. It is well known that the total radar return signal reflected by a target is composed of the vector sum of superimposed return signals from the individual parts of the target.
Movement of the target and its integrated parts with respect to the tracking radar system may cause the total return signal to change with time. These changes in the total return signal are exhibited as perturbations or target noise in the measured parameters of the target. One type of target noise is referred to as angle noise and is discussed in further deail in Radar Handbook, 1970, McGraw-Hill, Inc., Chapter 28 at Pages 28-1 through 28-15.
The measured angular position of an apparent source of the return signal reflected from a target is dependent upon the relative phase and amplitude of the component return signals and their relative angular positions. Target movement can cause the apparent source of the total return signal to move about a reference point on the target. Angle noise due to target movement, also known as glint, results in a change with time of the apparent location of the target with respect to the target reference point, typically the target centroid, i.e., the “center of gravity” of the distribution of the target reflecting areas. It should be noted that the target centroid is typically the long-time-averaged tracking point on the target.
Angular noise, in certain cases, may result in the measured or apparent angular position of the target to fall outside the actual physical boundaries of the target. In applications where precise measurement of the target is required, angular noise may adversely affect the measurement of the target location. For example, where the radar tracking system is located on a tactical missile and integrated into a LOS rate tracking loop, error caused by angular noise may result in a missile failing to intercept the tracked target.
It is, therefore, an object of the present invention to provide a new and improved method and system for adaptively reducing the affect of angular noise in a target radar return signal.
It is yet another object of the invention to provide a method and system for adaptively reducing, in a displacement signal having a value indicative of a measured angular displacement between an antenna electrical boresight and an apparent line of sight to a target, a noise signal having a value indicative of an angular error induced by a shift in the target radar centroid so as to provide a signal having a value indicative of an estimate of a true angular displacement between the antenna boresight and a true line of sight to the target.